The present application relates to a method of manufacturing a cathode active material, and more particularly, to a method of manufacturing a cathode active material having a composite oxide material containing lithium (Li) and nickel (Ni).
Recently, as portable devices such as a video camera and a laptop personal computer are widely used, small-sized high-capacity secondary batteries are highly demanded. In the past, a nickel-hydrogen battery or a nickel-cadmium battery containing an alkali electrolyte solution has been used as a secondary battery. However, since they have a low battery voltage of about 1.2 V, it was difficult to improve an energy density. For this reason, a lithium metal secondary battery which adopts lithium as an anode material has been proposed. It has been known that lithium has a lightest weight among single solid materials (its specific gravity is 0.534) and produces a significantly low voltage and a largest current amount per unit weight among metal anode materials.
However, in the secondary battery adopting lithium as an anode material, resin-like lithium (i.e., dendrite) is precipitated on a surface of the anode during a charge operation, and the dentrite grows as the charge/discharge cycle is repeated. This dentrite growth deteriorates a charge/discharge cycle characteristic of the secondary battery, and may, in a worst case, generate damages to a barrier membrane (separator) arranged to prevent contact between the positive and anodes and produce an internal short circuit. As a result, a battery may be fired and broken down.
For example, Japanese Patent Application Laid-open (JP-A) No. 62-90863 discloses another secondary battery which adopts a carbon material such as cokes as an anode and repeats the charge/discharge operation by doping and removing alkali metal ions. It was recognized that the aforementioned deterioration of the anode caused by the repeated charge/discharge operation could be prevented by adopting the secondary battery disclosed in the above-referenced patent document.
On the other hand, a cathode active material that can produce a high voltage has been studied and developed, and finally, an active material that can produce a battery voltage of about 4 V has been found and highlighted. It has been known that transition metal oxides including alkali metal or inorganic compounds such as transition metal chalcogen may be used as an active material. Among them, lithium transition metal composite oxides [LixNiO2(0<x≦1.0) or LixCoO2(0<x≦1.0)] containing nickel or cobalt as a main composition are most prospective from the viewpoints of a high voltage, safety, and a long lifetime. Among them, a cathode active material containing lithium nickelate (LiNiO2) as a main composition is expected to produce a relatively high voltage, a high charge current capacity, and a high energy density.
Currently, it is demanded to improve a capacity of a secondary battery which uses the lithium transition metal composite oxide as a cathode active material by modifying the lithium transition metal composite oxide containing nickel or cobalt as a main composition which is expected to produce a high charge current capacity and a high energy density. Also, it is demanded to improve charge/discharge efficiency of a secondary battery by modifying the lithium transition metal composite oxide.
In this regard, a method of reforming the cathode active material has been performed by coating other materials on surfaces of the composite oxide particles including lithium nickelate as a start material.
The aforementioned technology for reforming the cathode active material by coating the surface is necessary to provide a high coatability. In order to provide the high coatability, various techniques have been proposed. For example, in a so-called dry deposition method, the composite oxide particles and coating materials are mixed and then baked. In addition, in a so-called wet deposition method, the coating materials are deposited by a metal hydroxide having a higher coatability. An example of the method of depositing the coating materials by the metal hydroxide is disclosed in JP-A No. 9-265985, in which cobalt (Co) and manganese (Mn) are deposited on the surfaces of the lithium nickelate (LiNiO2) particles using hydroxide deposition method thereof.